Analysis of the mechanisms of electron recombination in HgCdTe infrared photodiode

This paper presents an experimental study of minority carrier lifetime and recombination mechanisms in HgCdTe photodiode. The excitation light source is a wavelength-tunable pulsed infrared laser. A constant background illumination has been introduced to minimize the effect of the junction equivalent capacitor and resistance. The decay of the photo-generated voltage is recorded by a storage oscilloscope. By fitting the exponentially decay curve, the time constant has been obtained which is regarded as the photo-generated minority carrier lifetime of the HgCdTe photodiode. The experimental results show that the carrier lifetime is in the range of 18–407 ns at 77 K for the measured detectors of four Cd compositions. It was found that the Auger recombination process is more effective for low Cd composition while the radiative recombination process became more important for high composition materials. The Shockley–Read–Hall recombination processes could not be ignored for all Cd composition.     

Measurements of the cross section for e(+)e(-) --> hadrons at center-of-mass energies from 2 to 5 GeV

We report values of R = sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->mu(+)mu(-)) for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.     

Viscosity and stress autocorrelation function in supercooled water: a molecular dynamics study

Following Guo, G.-J., and Zhang, Y.-G., 2001, Molec. Phys., 99, 283, which calculates the bulk and shear viscosities of SPC/E water at 30°C and 0.999 g cm^?3, further molecular dynamics simulations have been performed at state points of 0°C, ?20°C, ?40°C, and ?60°C along an approximate isobar with the previous state point. SACF and BACF (stress autocorrelation functions related to shear and bulk viscosities, respectively) of high precision have been obtained and compared for their similarities and differences. Shear and bulk viscosities calculated from them showed an increased deviation from real water with decreasing temperature. These correlation functions were then fitted using a uniform two-step relaxation function including a fast oscillatory Kohlrausch law and a slow straightforward Kohlrausch law. The fitting parameters of SACF and BACF have been analysed in detail, and several interesting dynamic phenomena were observed. (1) The oscillation frequency of SACF (44 ~ 48ps^?1) for short time intervals agrees with the stretching mode of hydrogen bonds, while that of BACF (7 ~ 12ps^?1) agrees with the bending mode of hydrogen bonds. (2) With decreasing temperature, the slow relaxation fraction of the BACF increases, while that of the SACF remains constant. (3) The exponents β in the Kohlrausch laws with values greater than 1 are obtained for BACF at ambient temperatures. (4) With regard to both shear and bulk viscosities, the slow relaxation time largely increases with decreasing temperature, while the fast relaxation time slightly decreases. These phenomena are qualitatively explained and discussed.     

Control of gain and thermal carrier loss profiles for mode optimization in 980-nm broad-area vertical-cavity surface-emitting lasers

Optical gain and thermal carrier loss distributions regarding current diffusion and various electric contact areas are investigated to improve the near-field modes from the ring-shape to a Gaussian-like configuration for extra-broad-area and oxide-confined vertical-cavity surface-emitting lasers. In this work an equivalent circuit network model is used. The resistance of the continuously-graded distributed Bragg reflectors （DBRs）, the current diffusion and the temperature effect due to different electric-contact areas are calculated and analyzed at first, as these parameters affect one another and are the key factors in determining the gain and thermal carrier loss. Finally, the gain and thermal carrier loss distributions are calculated and discussed.     

Multipacting analysis in micro-pulse electron gun

Modeling multipacting to steady state saturation is of interest in determining the performance of the micro-pulse electron gun. In this paper, a novel method is proposed to calculate the multipacting resonance param- eters for the gun. This method works well, and the 2-D simulation results suggest that steady state saturation can be achieved in the gun. After saturation the transition from two-surface multipacting to single-surface multipacting occurred, and an extensive range of electron emission time is a suggested way to avoid this kind of transition.     

相同雷诺数和尖速比下缩比风力机流动特性分析

针对NREL PhaseⅥ（D=10.058 m）风力机及其两个缩比模型（D=1.5 m和D=1 0 m）在叶片表面理想光滑状态,相同雷诺数(Re_{C（0.75R）≤7.42×10⁵}和尖速比（λ≤10.00）下,CFD计算得到的功率系数和推力系数不同展开原因调查,通过比较和分析各模型的流场信息,揭示了引起气动特性差异的主要原因,同时采用修正缩比模型入流风速的方法得到了与原型功率系数一致的入流风速修正系数。     

Accelerated steered response power method for sound source localization via clustering search

The steered response power-phase transform (SRP-PHAT) sound source localization algorithm is robust in a real environment. However, the large computation complexity limits the practical application of SRP-PHAT. For a microphone array, each location corresponds to a set of time differences of arrival (TDOAs), and this paper collects them into a TDOA vector. Since the TDOA vectors in the adjacent regions are similar, we present a fast algorithm based on clustering search to reduce the computation complexity of SRP-PHAT. In the training stage, the K-means or Iterative Self-Organizing Data Analysis Technique (ISODATA) clustering algorithm is used to find the centroid in each cluster with similar TDOA vectors. In the procedure of sound localization, the optimal cluster is found by comparing the steered response powers (SRPs) of all centroids. The SRPs of all candidate locations in the optimal cluster are compared to localize the sound source. Experiments both in simulation environments and real environments have been performed to compare the localization accuracy and computational load of the proposed method with those of the conventional SRP-PHAT algorithm. The results show that the proposed method is able to reduce the computational load drastically and maintains almost the same localization accuracy and robustness as those of the conventional SRP-PHAT algorithm. The difference in localization performance brought by different clustering algorithms used in the training stage is trivial.     

Wear analysis of revolute joints with clearance in multibody systems

In this work, the prediction of wear for revolute joint with clearance in multibody systems is investigated using a computational methodology. The contact model in clearance joint is established using a new hybrid nonlinear contact force model and the friction effect is considered by using a modified Coulomb friction model. The dynamics model of multibody system with clearance is established using dynamic segmentation modeling method and the computational process for wear analysis of clearance joint in multibody systems is presented. The main computational process for wear analysis of clearance joint includes two steps, which are dynamics analysis and wear analysis. The dynamics simulation of multibody system with revolute clearance joint is carried out and the contact forces are drawn and used to calculate the wear amount of revolute clearance joint based on the Archard’s wear model. Finally, a four-bar multibody mechanical system with revolute clearance joint is used as numerical example application to perform the simulation and show the dynamics responses and wear characteristics of multibody systems with revolute clearance joint. The main results of this work indicate that the contact between the joint elements is wider and more frequent in some specific regions and the wear phenomenon is not regular around the joint surface, which causes the clearance size increase non-regularly after clearance joint wear. This work presents an effective method to predict wear of revolute joint with clearance in multibody systems.